Bipolar junction transistor and method of manufacturing the same

ABSTRACT

A bipolar junction transistor includes a first trench element isolation film, a second trench element isolation film, a first base region, a second base region, a collector region, a first well, a second well, an emitter, a collector, and bases. The second well is formed by implanting an n-type impurity into the semiconductor substrate, and the emitter is formed by implanting the n-type impurity into the emitter region between the first trench element isolation film and the second well. The collector is formed by implanting the n-type impurity into the collector region between the first well and the second trench element isolation film, and the bases are formed by implanting the p-type impurity into the first base region and into the second base region between the emitter region and the second well.

The present application claims priority to Korean Patent Application No.10-2011-0086401 (filed on Aug. 29, 2011), which is hereby incorporatedby reference in its entirety.

BACKGROUND

Generally, a bipolar junction transistor improves in currentperformance, speed, and gain as compared to a metal oxide semiconductortransistor, and is thus widely used when designing an analog power RFIC.

A bipolar junction transistor having an emitter, a base, and a collectoris classified into a vertical bipolar junction transistor and a lateralbipolar junction transistor depending on the traveling direction ofelectric charges emitted from the emitter.

The bipolar junction transistor is used as an electrostatic dischargeprotection element which protects an internal IC circuit.

FIG. 1 is a sectional view illustrating a lateral bipolar junctiontransistor as an electrostatic discharge protection element in therelated art. FIG. 1 shows an npn-type bipolar junction transistor.

As illustrated in FIG. 1, a bipolar junction transistor for anelectrostatic discharge protection element in the related art includes afirst trench element isolation film 14, a second trench elementisolation film 15, and a third trench element isolation film 16 whichare formed on a p-type semiconductor substrate 11, and define an emitterregion, a base region, and a collector region.

A p-type impurity is implanted into the emitter region and the baseregion including the first trench element isolation film 14 of thesemiconductor substrate 11 to form a first well 12.

An n-type impurity is implanted into the collector region including thethird trench element isolation film 16 of the semiconductor substrate 11to form a second well 13.

A p-type impurity is implanted into the base region between the firsttrench element isolation film 14 and the second trench element isolationfilm 15 to form a base 19.

An n-type impurity is implanted into the collector region between thefirst well 12 and the third trench element isolation film 16 to form acollector 18.

An n-type impurity is implanted into the emitter region isolated fromthe base region by the first trench element isolation film 14 to form anemitter 17.

When the bipolar junction transistor is used as an electrostaticdischarge protection element, an input/output (I/O) terminal should beconstituted at the time of circuit design. The collector is connected tothe input/output terminal, the emitter is connected to the groundterminal, and the base is connected to the ground terminal through aresistor.

The bipolar junction transistor for an electrostatic dischargeprotection element is used to protect a semiconductor device from staticelectricity. If an electrostatic voltage equal to or higher than 2000 Vis input to the input/output terminal, the bipolar junction transistorrapidly discharges an electrostatic current to the ground terminal. Forthis reason, in order to use the bipolar junction transistor as anelectrostatic discharge protection element, the parameters, such as atriggering voltage Vt, a holding voltage Vh, and a breakdown voltage Vb,must be satisfied.

On the other hand, a lateral bipolar junction transistor exhibitsunsatisfactory characteristics as compared to a vertical bipolarjunction transistor from the viewpoint of electrostatic dischargeprotection performance.

Accordingly, in the related art, as illustrated in a sectional view ofFIG. 2, the positions of the emitter 17 and the base 19 are reversed. Asillustrated in FIG. 2, if the positions of the emitter and the base arereversed, the tunneling effect of the bipolar junction transistorappears faster than that of FIG. 1, such that the triggering time can beadvanced.

However, even when the positions of the emitter and the base arereversed, it is difficult to secure a satisfactory electrostaticdischarge protection. For this reason, the size of the bipolar junctiontransistor must still be increased.

The increase in the size of the bipolar junction transistor leads to anincrease in the size of the semiconductor device. Accordingly, there isa limit to which the size of the bipolar junction transistor may beincreased before it becomes undesirable.

SUMMARY

Embodiments relate to a bipolar junction transistor (BJT), and moreparticularly, to a bipolar junction transistor and a method ofmanufacturing the same capable of improving electrostatic dischargeprotection performance without causing an increase in the size of alateral bipolar junction transistor as an electrostatic dischargeprotection element.

Embodiments relate to changing the structure of a lateral bipolarjunction transistor as an electrostatic discharge protection element toimprove electrostatic discharge protection performance without aresulting increase in size.

Embodiments relate to a method of manufacturing a lateral bipolarjunction transistor as an electrostatic discharge protection element.

In accordance with embodiments, there is provided a bipolar junctiontransistor including: a first trench element isolation film and a secondtrench element isolation film which are formed on and/or over a p-typesemiconductor substrate, and which define an emitter region, a firstbase region, a second base region, and a collector region; a first wellwhich is formed by implanting a p-type impurity into the semiconductorsubstrate including the first trench element isolation film, the emitterregion, the first base region, and the second base region; a second wellwhich is formed by implanting an n-type impurity into the semiconductorsubstrate including the second trench element isolation film and thecollector region; an emitter which is formed by implanting the n-typeimpurity into the emitter region between the first trench elementisolation film and the second well; a collector which is formed byimplanting the n-type impurity into the collector region between thefirst well and the second trench element isolation film; and bases whichare formed by implanting the p-type impurity into the first base regionisolated from the emitter region by the first trench element isolationfilm and into the second base region between the emitter region and thesecond well.

In accordance with embodiments, there is provided a bipolar junctiontransistor including: a first trench element isolation film and a secondtrench element isolation film which are formed on and/or over a p-typesemiconductor substrate, and define an emitter region, a first baseregion, a second base region, and a collector region; a first well whichis formed by implanting a p-type impurity into the semiconductorsubstrate including the first trench element isolation film, the emitterregion, the first base region, and the second base region; a second wellwhich is formed by implanting an n-type impurity into the semiconductorsubstrate including the second trench element isolation film and thecollector region; bases which are formed by implanting the p-typeimpurity into the first base region and the second base region arrangedin order between the first trench element isolation film and the secondwell; a collector which is formed by implanting the n-type impurity intothe collector region between the first well and the second trenchelement isolation film; an emitter which is formed by implanting then-type impurity into the emitter region isolated from the first baseregion by the first trench element isolation film; and a third wellwhich is formed by implanting the p-type impurity into the first well tosurround the second base region; and implanting the n-type impurity intothe second cell to form a fourth well below the collector region and thesecond trench element isolation film.

The bipolar junction transistor may further include a fifth well whichis formed along the boundary of the semiconductor substrate byimplanting the n-type impurity from below the third well and to belowthe fourth well.

The bipolar junction transistor may further include a third trenchelement isolation film which is formed between the first base region andthe second base region.

In accordance with embodiments, there is provided a method ofmanufacturing a bipolar junction transistor, the method including:forming a first trench element isolation film and a second trenchelement isolation film on and/or over a p-type semiconductor substrateto define an emitter region, a first base region, a second base region,and a collector region; implanting a p-type impurity into thesemiconductor substrate including the first trench element isolationfilm, the emitter region, and the base region to form a first well;implanting an n-type impurity into the semiconductor substrate includingthe second trench element isolation film and the collector region toform a second well; implanting the n-type impurity into the emitterregion between the first trench element isolation film and the secondwell to form an emitter; implanting the n-type impurity into thecollector region between the first well and the second trench elementisolation film to form a collector; and implanting the p-type impurityinto the first base region isolated from the emitter region by the firsttrench element isolation film and into the second base region betweenthe emitter region and the second well to form bases.

Embodiments may further include, after forming of the first well,implanting the p-type impurity into the first well to form a third wellto surround the second base region; and after forming of the secondwell, implanting the n-type impurity into the second well to form afourth well below the collector region and the second trench elementisolation film.

Embodiments may further include implanting the n-type impurity frombelow the third well to below the fourth well to form a fifth well alongthe boundary of the semiconductor substrate.

Embodiments may further include forming a third trench element isolationfilm between the emitter region and the second base region.

In accordance with embodiments, there is provided a method ofmanufacturing a bipolar junction transistor, the method including:forming a first trench element isolation film and a second trenchelement isolation film on and/or over a p-type semiconductor substrateto define an emitter region, a first base region, a second base region,and a collector region; implanting a p-type impurity into thesemiconductor substrate including the first trench element isolationfilm, the emitter region, the first base region, and the second baseregion to form a first well; implanting the p-type impurity into thefirst well to form a third well to surround the second base region;implanting an n-type impurity into the semiconductor substrate includingthe second trench element isolation film and the collector region toform a second well; implanting the n-type impurity into the second wellto form a fourth well below the collector region and the second trenchelement isolation film; implanting the p-type impurity into the firstbase region and the second base region arranged in order between thefirst trench element isolation film and the second well to form bases;implanting the n-type impurity into the collector region between thefirst well and the second trench element isolation film to form acollector; and implanting the n-type impurity into the emitter regionisolated from the first base region by the first trench elementisolation film to form an emitter.

Embodiments may further include, prior to forming the base, implantingthe n-type impurity from below the third well to below the fourth wellto form a fifth well along the boundary of the semiconductor substrate.

Embodiments may further include, prior to forming the first well,forming a third trench element isolation film between the first baseregion and the second base region.

In accordance with embodiments, the triggering voltage can be easilyadjusted to improve the capability to decrease the triggering voltage,base resistance can be reduced to increase the holding voltage, and adeep current path to the lower end of the base can be formed. Therefore,it is possible to improve electrostatic discharge protection performancewithout causing an increase in the size of the bipolar junctiontransistor.

DRAWINGS

FIG. 1 is a sectional view illustrating a lateral bipolar junctiontransistor as an electrostatic discharge protection element in therelated art.

FIG. 2 is a sectional view illustrating a lateral bipolar junctiontransistor as an electrostatic discharge protection element in therelated art.

Example FIG. 3 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 4 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 5 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 6 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 7 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 8 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 9 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 10 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 11 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 12 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

Example FIG. 13 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments.

DESCRIPTION

Advantages and features of the invention and methods of accomplishingthe same may be understood more readily by reference to the followingdetailed description of embodiments and the accompanying drawings. Theinvention may, however, be embodied in many different forms and shouldnot be construed as being limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bemore readily understood by those skilled in the art, and the inventionwill only be defined by the appended claims.

Example FIG. 3 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 3 illustrates an npn-type bipolarjunction transistor.

As illustrated in Example FIG. 3, the bipolar junction transistoraccording to embodiments includes a first trench element isolation film104 and a second trench element isolation film 106 which are formed onand/or over a p-type semiconductor substrate 101 to define an emitterregion, a first base region, a second base region, and a collectorregion, a first well 102 which is formed by implanting p-type impurityions into the semiconductor substrate 101 including the emitter region,the first base region, and the second base region, a second well 103which is formed by implanting n-type impurity ions into thesemiconductor substrate 101 including the second trench elementisolation film 106 and the collector region, an emitter 107 which isformed by implanting the n-type impurity ions into the emitter regionbetween the first trench element isolation film 104 and the second well103, a collector 108 which is formed by implanting the n-type impurityions into the collector region between the first well 102 and the secondtrench element isolation film 106, and bases 109 and 201 which areformed by implanting the p-type impurity ions into the first base regionisolated from the emitter region by the first trench element isolationfilm 104 and into the second base region between the emitter region andthe second well 103.

A process for manufacturing the bipolar junction transistor according toembodiments will now be described in detail with reference to exampleFIG. 3.

First, the first trench element isolation film 104 and the second trenchelement isolation film 106 are formed on and/or over the p-typesemiconductor substrate 101 to define the emitter region, the first baseregion, the second base region, and the collector region.

Next, the p-type impurity ions are implanted into the semiconductorsubstrate 101 including the first trench element isolation film 104, theemitter region, and the first and second base regions to form the firstwell 102, and the n-type impurity ions are implanted into thesemiconductor substrate 101 including the second trench elementisolation film 106 and the collector region to form the second well 103.

Next, the n-type impurity ions are implanted into the emitter regionbetween the first trench element isolation film 104 and the second well103 to form the emitter 107.

The n-type impurity ions are implanted into the collector region betweenthe first well 102 and the second trench element isolation film 106 toform the collector 108.

The p-type impurity ions are implanted into the first base regionisolated from the emitter region where the emitter 107 is formed by thefirst trench element isolation film 104 and into the second base regionbetween the emitter region where the emitter 107 is formed and thesecond well 103 to form the bases 109 and 201.

When comparing the bipolar junction transistor of example FIG. 3according to embodiments with the bipolar junction transistor of FIG. 2according to the related art, it can be seen that the second trenchelement isolation film 15 in the boundary region of the P-type well 12and the N-type 13 is removed, and the base 201 is further formed in thesecond base region of the first well 102.

In the bipolar junction transistor according to embodiments, thepositions of the emitter 107 and the base 109 are changed, and thetunneling effect appears rapidly as compared to the bipolar junctiontransistor of FIG. 1 according to the related art, such that thetriggering time can be advanced. The triggering voltage Vt can beadjusted by the first well 102, the second well 103, and the base 201,thereby improving the capability to decrease the triggering voltage Vt.

With the addition of the base 201, base resistance is reduced, resultingin an increase in the holding voltage Vh.

In a structure in which no base 201 is added, electrons emitted from theemitter 107 are crowded on the surfaces of the first well 102 and thesecond well 103. Meanwhile, with the addition of the base 201, a deepcurrent path to the lower end of the base 201 is formed. The deepcurrent path results in an increase in the breakdown voltage Vh.

Example FIG. 4 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 4 illustrates a pnp type which isa modification to the bipolar junction transistor illustrated in FIG. 3.

Example FIG. 5 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 5 illustrates an npn-type bipolarjunction transistor.

As illustrated in example FIG. 5, the bipolar junction transistoraccording to embodiments includes a first trench element isolation film104 and a second trench element isolation film 106 which are formed onand/or over a p-type semiconductor substrate 101 to define an emitterregion, a first base region, a second base region, and a collectorregion, a first well 102 which is formed by implanting p-type impurityions into the semiconductor substrate 101 including the emitter region,the first base region, and the second base region, a second well 103which is formed by implanting n-type impurity ions into thesemiconductor substrate 101 including the second trench elementisolation film 106 and the collector region, an emitter 107 which isformed by implanting the n-type impurity ions into the emitter regionbetween the first trench element isolation film 104 and the second well103, a collector 108 which is formed by implanting the n-type impurityions into the collector region between the first well 102 and the secondtrench element isolation film 106, bases 109 and 201 which are formed byimplanting the p-type impurity ions into the first base region isolatedfrom the emitter region by the first trench element isolation film 104and into the second base region between the emitter region and thesecond well 103, a third well 202 which is formed by implanting thep-type impurity ions into the first well 102 to surround the base 201(second base region), and a fourth well 203 which is formed below thecollector 108 (collector region) and the second trench element isolationfilm 106 by implanting the n-type impurity ions into the second well103.

A process of manufacturing the bipolar junction transistor according toembodiments is described as follows.

First, the first trench element isolation film 104 and the second trenchelement isolation film 106 are formed on and/or over the p-typesemiconductor substrate 101 to define the emitter region, the first baseregion, the second base region, and the collector region.

Next, the p-type impurity ions are implanted into the semiconductorsubstrate 101 including the first trench element isolation film 104, theemitter region, and the first and second base regions to form the firstwell 102, and the p-type impurity ions are implanted into the first well102 to form the third well 202 to surround the second base region wherethe base 201 will be formed in a subsequent step.

Next, the n-type impurity ions are implanted into the semiconductorsubstrate 101 including the second trench element isolation film 106 andthe collector region to form the second well 103, and the n-typeimpurity ions are implanted into the second well 103 to form the fourthwell 203 below the collector region where the collector 108 will beformed in a subsequent step and the second trench element isolation film106.

Next, the n-type impurity ions are implanted into the emitter regionbetween the first trench element isolation film 104 and the second well103 to form the emitter 107.

The n-type impurity ions are implanted into the collector region betweenthe first well 102 and the second trench element isolation film 106 toform the collector 108.

The p-type impurity ions are implanted into the first base regionisolated from the emitter region where the emitter 107 is formed by thefirst trench element isolation film 104 and into the second base regionbetween the emitter region where the emitter 107 is formed and thesecond well 103 to form the bases 109 and 201.

When comparing the bipolar junction transistor illustrated in exampleFIG. 5 according to embodiments with the bipolar junction transistorillustrated in example FIG. 3, it can be seen that the third well 202and the fourth well 203 are further formed.

In the bipolar junction transistor according to embodiments, thetriggering voltage Vt can be adjusted by the first well 102, the secondwell 103, the third well 202, and the base 201 as compared to thebipolar junction transistor illustrated in example FIG. 3, furtherimproving the capability to decrease the triggering voltage Vt.

Example FIG. 6 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 6 illustrates a pnp type which isa modification to the bipolar junction transistor illustrated in exampleFIG. 5.

Example FIG. 7 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 7 illustrates an npn-type bipolarjunction transistor.

As illustrated in example FIG. 7, the bipolar junction transistoraccording to embodiments includes a first trench element isolation film104 and a second trench element isolation film 106 which are formed onand/or over a p-type semiconductor substrate 101 to define an emitterregion, a first base region, a second base region, and a collectorregion, a first well 102 which is formed by implanting p-type impurityions into the semiconductor substrate 101 including the emitter region,the first base region, and the second base region, a second well 103which is formed by implanting n-type impurity ions into thesemiconductor substrate 101 including the second trench elementisolation film 106 and the collector region, an emitter 107 which isformed by implanting the n-type impurity ions into the emitter regionbetween the first trench element isolation film 104 and the second well103, a collector 108 which is formed by implanting the n-type impurityions into the collector region between the first well 102 and the secondtrench element isolation film 106, bases 109 and 201 which are formed byimplanting the p-type impurity ions into the first base region isolatedfrom the emitter region by the first trench element isolation film 104and into the second base region between the emitter region and thesecond well 103, a third well 202 which is formed by implanting thep-type impurity ions into the first well 102 to surround the base 201(second base region), a fourth well 203 which is formed below thecollector 108 (collector region) and the second trench element isolationfilm 106 by implanting the n-type impurity ions into the second well103, and a fifth well 204 which is formed along the boundary of thesemiconductor substrate 101 by implanting the n-type impurity ions frombelow the third well 202 to below the fourth well 203.

A process for manufacturing the bipolar junction transistor according toembodiments will now be described in detail with reference to exampleFIG. 7.

First, the first trench element isolation film 104 and the second trenchelement isolation film 106 are formed on and/or over the p-typesemiconductor substrate 101 to define the emitter region, the first baseregion, the second base region, and the collector region.

Next, the p-type impurity ions are implanted into the semiconductorsubstrate 101 including the first trench element isolation film 104, theemitter region, and the first and second base regions to form the firstwell 102, and the p-type impurity ions are implanted into the first well102 to form the third well 202 to surround the second base region wherethe base 201 will be formed in a subsequent step.

Next, the n-type impurity ions are implanted into the semiconductorsubstrate 101 including the second trench element isolation film 106 andthe collector region to form the second well 103, and the n-typeimpurity ions are implanted into the second well 103 to form the fourthwell 203 below the collector region where the collector 108 will beformed in a subsequent step and the second trench element isolation film106.

Next, the n-type impurity ions are implanted deeply from below the thirdwell 202 to below the fourth well 203 to form the fifth well 204 alongthe boundary of the semiconductor substrate 101.

Next, the n-type impurity ions are implanted into the emitter regionbetween the first trench element isolation film 104 and the second well103 to form the emitter 107.

The n-type impurity ions are implanted into the collector region betweenthe first well 102 and the second trench element isolation film 106 toform the collector 108.

The p-type impurity ions are implanted into the first base regionisolated from the emitter region where the emitter 107 is formed by thefirst trench element isolation film 104 and into the second base regionbetween the emitter region where the emitter 107 is formed and thesecond well 103 to form the bases 109 and 201.

When comparing the bipolar junction transistor illustrated in exampleFIG. 7 according to embodiments with the bipolar junction transistorillustrated in example FIG. 5, it can be seen that the fifth well 204 isfurther formed.

When comparing the bipolar junction transistor as illustrated in exampleFIG. 7 according to embodiments with the bipolar junction transistorillustrated in example FIG. 5, electrons emitted from the emitter 107form a deep current path to the lower end of the base 201 along thefifth well 204.

Example FIG. 8 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 8 illustrates an npn-type bipolarjunction transistor.

As illustrated in example FIG. 8, the bipolar junction transistoraccording to embodiments includes a first trench element isolation film104, a second trench element isolation film 106, and a third trenchelement isolation film 205 which are formed on and/or over a p-typesemiconductor substrate 101 to define an emitter region, a first baseregion, a second base region, and a collector region, a first well 102which is formed by implanting p-type impurity ions into thesemiconductor substrate 101 including the emitter region, the first baseregion, and the second base region, a second well 103 which is formed byimplanting n-type impurity ions into the semiconductor substrate 101including the second trench element isolation film 106 and the collectorregion, an emitter 107 which is formed by implanting the n-type impurityions into the emitter region between the first trench element isolationfilm 104 and the third trench element isolation film 205, a collector108 which is formed by implanting the n-type impurity ions into thecollector region between the first well 102 and the second trenchelement isolation film 106, bases 109 and 201 which are formed byimplanting the n-type impurity ions into the first base region isolatedfrom the emitter region by the first trench element isolation film 104and into the second base region between the third trench elementisolation film 205 and the second well 103, a third well 202 which isformed by implanting the p-type impurity ions into the first well 102 tosurround the base 201 (second base region), a fourth well 203 which isformed below the collector 108 (collector region) and the second trenchelement isolation film 106 by implanting the n-type impurity ions intothe second well 103.

A process for manufacturing the bipolar junction transistor according toembodiments will now be described in detail with reference to exampleFIG. 8.

First, the first trench element isolation film 104, the second trenchelement isolation film 106, and the third trench element isolation film205 are formed on and/or over the p-type semiconductor substrate 101 todefine the emitter region, the first base region, the second baseregion, and the collector region.

Next, the p-type impurity ions are implanted into the semiconductorsubstrate 101 including the first trench element isolation film 104, theemitter region, and the first and second base regions to form the firstwell 102, and the p-type impurity ions are implanted into the first well102 to form the third well 202 to surround the second base region wherethe base 201 will be formed in a subsequent step.

Next, the n-type impurity ions are implanted into the semiconductorsubstrate 101 including the second trench element isolation film 106 andthe collector region to form the second well 103, and the n-typeimpurity ions are implanted into the second well 103 to form the fourthwell 203 below the collector region where the collector 108 will beformed in a subsequent step and the second trench element isolation film106.

Next, the n-type impurity ions are implanted into the emitter regionbetween the first trench element isolation film 104 and the third trenchelement isolation film 205 to form the emitter 107.

The n-type impurity ions are implanted into the collector region betweenthe first well 102 and the second trench element isolation film 106 toform the collector 108.

The p-type impurity ions are implanted into the first base regionisolated from the emitter region where the emitter 107 is formed by thefirst trench element isolation film 104 and into the second base regionbetween the third trench element isolation film 205 and the second well103 to form the bases 109 and 201.

When comparing the bipolar junction transistor illustrated in exampleFIG. 8 according to embodiments with the bipolar junction transistorillustrated in example FIG. 5, it can be seen that the third trenchelement isolation film 205 is further formed.

With comparing the bipolar junction transistor according to embodimentsas illustrated in example FIG. 8 with the bipolar junction transistorillustrated in example FIG. 5, junction breakdown does not appear on thesurface and occurs below the third trench element isolation film 205,such that element reliability is relatively improved.

Example FIG. 9 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 9 is a pnp type which is amodification to the bipolar junction transistor illustrated in exampleFIG. 8.

Example FIG. 10 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. In the bipolar junction transistor illustratedin example FIG. 10, a fifth well 204 is further formed in the bipolarjunction transistor illustrated in example FIG. 8. The bipolar junctiontransistor including the fifth well 204 has been described withreference to example FIG. 7, thus detailed description thereof will notbe repeated.

In embodiments described with reference to example FIGS. 5, 6, 7, 8, 9,and 10, the positions of the emitter 107 and the base 109 may bereversed. Some modifications of embodiments will be described withreference to example FIGS. 11 to 13.

Example FIG. 11 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. Example FIG. 11 illustrates a modification inwhich the positions of the emitter 107 and the base 109 in the bipolarjunction transistor of example FIG. 5 are reversed.

As illustrated in example FIG. 11, the lateral bipolar junctiontransistor according to embodiments includes a first trench elementisolation film 104 and a second trench element isolation film 106 whichare formed on and/or over a p-type semiconductor substrate 101 to definean emitter region, a first base region, a second base region, and acollector region, first trench element isolation film 104, the emitterregion, a first well 102 which is formed by implanting p-type impurityions into the semiconductor substrate 101 including the first baseregion and the second base region, a second well 203 which is formed byimplanting n-type impurity ions into the semiconductor substrate 101including the second trench element isolation film 106 and the collectorregion, bases 109 and 201 which are formed by implanting the p-typeimpurity ions into the first base region and the second base regionarranged in order between the first trench element isolation film 104and the second well 103, a collector 108 which is formed by implantingthe n-type impurity ions into the collector region between the firstwell 102 and the second trench element isolation film 106, an emitter107 which is formed by implanting the n-type impurity ions into theemitter region isolated from the first base region by the first trenchelement isolation film 104, a third well 202 which is formed byimplanting the p-type impurity ions into the first well 102 to surroundthe second base region, and a fourth well 203 which is formed below thecollector region and the second trench element isolation film 106 byimplanting the n-type impurity ions into the second well 103.

A process for manufacturing the bipolar junction transistor according toembodiments will now be described in detail with reference to exampleFIG. 11.

First, the first trench element isolation film 104 and the second trenchelement isolation film 106 are formed on and/or over the p-typesemiconductor substrate 101 to define the emitter region, the first baseregion, the second base region, and the collector region.

Next, the p-type impurity ions are implanted into the semiconductorsubstrate 101 including the first trench element isolation film 104, theemitter region, and the first and second base regions to form the firstwell 102, and the p-type impurity ions are implanted into the first well102 to form the third well 202 to surround the second base region wherethe base 201 will be formed in a subsequent step.

Next, the n-type impurity ions are implanted into the semiconductorsubstrate 101 including the second trench element isolation film 106 andthe collector region to form the second well 103, and the n-typeimpurity ions are implanted into the second well 103 to form the fourthwell 203 below the collector region where the collector 108 will beformed in a subsequent step and the second trench element isolation film106.

Next, the p-type impurity ions are implanted into the first base regionand the second base region arranged in order between the first trenchelement isolation film 104 and the second well 103 to form the bases 109and 201.

Next, the n-type impurity ions are implanted into the collector regionbetween the first well 102 and the second trench element isolation film106 to form the collector 108.

Finally, the n-type impurity ions are implanted into the emitter regionisolated from the base 109 (first base region) by the first trenchelement isolation film 104 to form the emitter 107.

Example FIG. 12 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. From example FIG. 12, it can be seen that afifth well 204 is further formed in the bipolar junction transistor ofexample FIG. 11. The bipolar junction transistor including the fifthwell 204 has been described with reference to example FIG. 7, thusdetailed description thereof will not be repeated.

Example FIG. 13 is a sectional view illustrating a lateral bipolarjunction transistor as an electrostatic discharge protection elementaccording to embodiments. From example FIG. 13, it can be seen that athird trench element isolation film 205 is further formed in the bipolarjunction transistor of example FIG. 12. The bipolar junction transistorincluding the third trench element isolation film 205 has been describedwith reference to example FIG. 8, thus detailed description thereof willnot be repeated.

While the invention has been shown and described with respect toembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the invention as defined in the following claims.

What is claimed is:
 1. An apparatus comprising: a first trench elementisolation film formed over a p-type semiconductor substrate; a secondtrench element isolation film formed over the semiconductor substrate; afirst well formed by implanting a p-type impurity into the semiconductorsubstrate; a second well formed by implanting an n-type impurity intothe semiconductor substrate; an emitter formed by implanting the n-typeimpurity into an emitter region between the first trench elementisolation film and the second well; a collector formed by implanting then-type impurity into a collector region between the first well and thesecond trench element isolation film; a first base formed by implantingthe p-type impurity into a first base region isolated from the emitterregion by the first trench element isolation film; a second base formedby implanting the p-type impurity into a second base region between theemitter region and the second well; and a third well formed byimplanting the p-type impurity into the first well to surround thesecond base region; and a fourth well formed below the collector regionand the second trench element isolation film by implanting the n-typeimpurity into the second well.
 2. The apparatus of claim 1, furthercomprising: a fifth well formed along a boundary of the semiconductorsubstrate by implanting the n-type impurity below the third well andbelow the fourth well.
 3. The apparatus of claim 2, further comprising:a third trench element isolation film formed between the emitter regionand the second base region.
 4. The apparatus of claim 1, furthercomprising: a third trench element isolation film formed between theemitter region and the second base region.
 5. An apparatus comprising: afirst trench element isolation film formed over a p-type semiconductorsubstrate; a second trench element isolation film formed over thesemiconductor substrate; a first well formed by implanting a p-typeimpurity into the semiconductor substrate; a second well formed byimplanting an n-type impurity into the semiconductor substrate; a firstbase formed by implanting the p-type impurity into a first base region;a second base formed by implanting the p-type impurity into a secondbase region; a collector formed by implanting the n-type impurity into acollector region between the first well and the second trench elementisolation film; an emitter formed by implanting the n-type impurity intoan emitter region that is isolated from the first base region by thefirst trench element isolation film; a third well formed by implantingthe p-type impurity into the first well to surround the second baseregion; and a fourth well formed below the collector region and thesecond trench element isolation film by implanting the n-type impurityinto the second well, wherein first base region and the second baseregion are arranged between the first trench element isolation film andthe second well.
 6. The apparatus of claim 5, further comprising: afifth well formed along a boundary of the semiconductor substrate byimplanting the n-type impurity below the third well and below the fourthwell.
 7. The apparatus of claim 6, further comprising: a third trenchelement isolation film formed between the first base region and thesecond base region.
 8. The apparatus of claim 5, further comprising: athird trench element isolation film formed between the first base regionand the second base region.